Exercise machines attempt to replicate work required by various muscles of the body to develop better physical fitness of those muscles and of the body in general. Since the early days of crude weight benches and simple stationary bicycles, exercise machines have been developed to be better for specific movements, more adaptable to a wider array of exercises, or more polished and advanced for easier production, marketing and distribution.
Some exercise machines have been developed to attempt to replicate a specific type of sport activity, such as biking, running, stair climbing, rowing and weight lifting. These machines offer variable resistance levels, computer program monitoring of vital statistics, and user-friendly control systems, all within a confined exercise space. However, typical sports activity-replicating machines such as stationary bikes, treadmills, stair-climbers, rowers, etc., can be only configured for one type of activity at a time.
Swimming, despite being one of the best forms of exercise, is one sport activity that is difficult to replicate on land due to the medium in which the original activity takes place. In water, a person is subjected to less gravitational force and substantially increased resistance in every direction under the surface of the water. Because of this medium, swimmers are known as having desirable physical attributes of more toned and balanced muscle mass, greater strength, and higher endurance than persons subjected to other forms of exercise or activity.